Scientific Forecaster Discussion
fxus66 klox 232037
Area forecast discussion...updated
National Weather Service Los Angeles/Oxnard California
137 PM PDT Sat Jun 23 2018
..aviation discussion updated...
Temperatures will cool off slightly, with extensive low clouds
and fog expected for the coast and valleys over the weekend. High
pressure will strengthen, bringing warmer temperatures and a
decrease in cloudiness for early next week.
Short term (tdy-tue)...23/916 am.
The marine inversion this morning ranged from 800 ft deep at vbg to
2400 ft deep at lax. Extensive low clouds covered the coast and vlys
this morning, especially S of Point Conception, as a decent southeast
flow in a fairly strong eddy covered the socal bight. The low
clouds are expected to clear to the coast north of Point Conception by
midday, and probably clear to just the coastal plain S of Point
Conception due to a persistent southeast to S flow over the socal bight
expected thru this afternoon. In addition, 12z NAM forecast
gradients at 00z this afternoon include +10.1 mb lax-dag and +6.8
mb lax-bfl. These strong onshore gradients will also help to keep
low clouds near or over the coastal plain today. Otherwise, mostly
sunny skies will prevail across the region. Highs are going to
be quite warm over the region again today, with the hottest
interior vlys and lower mtns expected to reach the 90s to around
102. For the vlys adjacent to the coast, highs should be mostly in
the 80s to around 90.
An upper level high off the srn California coast will persist in this area
thru sun, with very weak upper level troffiness expected over the
region tonight into Sun morning. Upper ridging will build back into
srn California Sun afternoon thru Mon. 500 mb heights thru the period are
generally expected to be rather high and in the 589-591 dm.
The marine layer will deepen some tonight into Sun morning to around
1500 ft north to 2500 ft or slightly hier S. Extensive marine layer
clouds and some fog can be expected for the coast and vlys tonight
into Sun morning. In addition, the persistent southeast to S flow at low
levels should help to contribute some upslope flow into the
foothills, with patchy drizzle not out of the question for the
coast, vlys and lower coastal slopes S of Point Conception. Will add
mention of patchy drizzle for these areas tonight into Sun morning
with the afternoon forecast package. The low clouds should clear to
the coast Sun afternoon, but may be persistent in a few areas such
as the Oxnard plain. There should be slightly lower marine inversion
Sun night, with low clouds and fog expected to return quickly to the
coast and vlys, then clear to or off the coast my midday Mon.
Otherwise, mostly clear skies will prevail over the forecast area
No major issues are anticipated with regards to winds through Monday.
Moderate to strong onshore gradients will generate the usual gusty
afternoon/evening southwesterly winds across the mountains and
deserts, but should be generally below advisory levels.
Temperatures are forecast to cool some sun, but remain several
degrees above normal for interior areas, then warm back up a few
degrees for most areas on Mon. Highs in the warmest interior vlys
and lower mtns sun should reach the mid 80s to lower 90s, except mid
90s to 101 in the Antelope Vly, then warm into the 90s Mon except
upper 90s to 103 in the Antelope Vly. For the vlys adjacent to the
coast, highs will be in the upper 70s to mid 80s sun and mid 80s to
around 90 on Mon.
Long term (wed-sat)...23/130 am.
For the extended, models continue to exhibit decent synoptic
agreement. At upper levels, ridge will peak in strength on Tuesday
and Wednesday then a decent trough will develop over the West
Coast Thursday and Friday. Near the surface, moderate to strong
onshore flow will continue with a bit of increase in northwesterly
flow Thursday and Friday.
Forecast-wise, things will still remain rather quiet through the
period. Marine inversion will fluctuate in depth through the
period (bit more shallow Tuesday/Wednesday then deepening
Thursday/friday), but should remain more than deep enough to push
into the coastal valleys each morning. Stratus dissipation each
afternoon should be good although some beach areas could be slow
to clear each afternoon. Other than the stratus, skies will remain
mostly clear. As for temperatures, Tuesday and Wednesday will be
the warmest days with a cooling trend Thursday and Friday. As for
winds, typical gusty onshore winds will continue across the
mountains and deserts. By Wednesday night, there may be some
increase in northerly winds across southern Santa Barbara County
and the Interstate 5 corridor, but nothing that appears too strong
at this time.
At 20z at klax... the inversion was around 2600 feet deep. The
top of the inversion was around 4400 feet with a temperature of
about 26 degrees celsius.
Overall north of Point Conception... moderate confidence in the
current tafs. LIFR/IFR conditions will develop along the coast and
into adjacent valleys 05z-10z then will linger through the
remaining forecast period. VFR conditions will prevail otherwise
and elsewhere including at kprb.
Overall south of Point Conception... low to moderate confidence
in the current tafs along the coast and in adjacent valleys with
high confidence in the current kpmd and kwjf tafs. IFR/MVFR
conditions will be slow to clear today and cigs may simply rise
into VFR criteria for a few hours rather than scatter or clear.
LIFR/IFR conditions will return to the coastal and adjacent valley
areas 01z-05z and will continue through the forecast period for
most terminals and through 20z-22z at klax. Otherwise and
elsewhere VFR conditions will prevail.
Klax... moderate confidence in the current taf. MVFR cigs have a
thirty percent chance of scattering/clearing today and a ten
percent chance of rising into VFR criteria for a few hours. MVFR
conditions will return 01z-05z and will continue through 20z-22z
with a thirty percent chance of IFR conditions during the period.
Otherwise VFR conditions will prevail. There is a eighty percent
chance of southeast winds greater than eight knots continuing
through the day. There is a sixty percent chance of gusts up to 20
kts continuing through 22z and a twenty five percent chance
Kbur... moderate confidence in the current taf. MVFR conditions will
be slow to clear today and cigs may simply rise into VFR criteria
for a few hours rather than scatter or clear. MVFR conditions will
return 01z-05z and will continue through the end of the forecast
period with a thirty percent chance of IFR conditions during the
period. Otherwise VFR conditions will prevail.
For the outer waters... Small Craft Advisory (sca) level winds
will continue through this afternoon for the central outer waters.
The winds in this zone will increase again overnight and into
tomorrow and the advisory may be extended or will be allowed to
expire and then reissued for the later period. The strongest winds
are around and south of Point Conception including the western
portion of the Santa Barbara Channel. Conditions in the northern
and southern outer waters will remain below Small Craft Advisory levels through
Wednesday though the winds and seas will be elevated at times.
For the inner waters north of Point Sal... conditions will remain
below Small Craft Advisory levels through Wednesday.
For the inner waters south of Point Conception... conditions will
remain below Small Craft Advisory levels through Wednesday. However... southeast
winds will be elevated late tonight and on Sunday with gusts
reaching Small Craft Advisory level at times. The winds will be strongest across
the western portion of the Santa Barbara Channel.
Fire weather...23/1142 am.
Strengthening onshore flow combined with a deepening marine layer
pattern will bring a gradual cooling trend for most areas, especially
coastal and valley areas. Temperatures will still remain very warm
today across interior sections, with some triple digit readings today
across the Antelope Valley and interior valleys of San Luis Obispo
County, with some cooling on Sunday. Humidities in these areas as
well as the mountains will fall into the 8 to 15 percent range today,
then trending higher on Sunday. Strengthening onshore winds will
add to the fire weather threat across interior sections today and
Sunday, with gusts generally ranging between 25 and 40 mph across
the mountains, deserts, and interior valleys, with isolated gusts
as high as 50 mph in the foothills of the Antelope Valley. As of
10 am, the lax-Daggett gradient is around +6 mb, and is expected
to peak around + 9 mb later this afternoon. The combination of very
warm and dry conditions combined with these strong onshore winds
will bring elevated fire danger through the weekend across the
mountains, deserts, and interior valleys of San Luis Obispo County,
with the potential for brief critical fire weather conditions
today. The greatest fire weather threat today and tomorrow will be
the Highway 14 corridor from Santa Clarita valley to the Antelope
Pz...Small Craft Advisory in effect until 3 PM PDT this afternoon
for zone 673. (See laxmwwlox).
Hazard potential outlook (tue-sat).
No significant hazards expected.